Operation of a forward link acknowledgement channel for the reverse link data

ABSTRACT

An acknowledgement method in a wireless communication system. Initially, a reverse supplemental channel (R-SCH) frame is received at a base station. The base station then transmits an acknowledgement (ACK) signal if quality of the received R-SCH frame is indicated as being good. A negative acknowledgement (NAK) signal is transmitted only if the received data frame is indicated as being bad but has enough energy such that, if combined with energy from retransmission of the data frame, it would be sufficient to permit correct decoding of the data frame. If the best base station is known, the acknowledgement method may reverse the transmission of the acknowledgement signals for the best base station so that only NAK signal is sent. A positive acknowledgement is assumed in the absence of an acknowledgement. This is done to minimize the transmit power requirements.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

This application is a continuation of U.S. patent application Ser. No.11/349,366, filed Feb. 6, 2006, allowed, entitled, “Operation of aForward Link Acknowledgement Channel for the Reverse Link Data” which isa Continuation of patent application Ser. No. 10/341,329, entitled“Operation of a Forward Link Acknowledgement Channel for the ReverseLink Data” filed Jan. 10, 2003, issued on Feb. 7, 2006 as U.S. Pat. No.6,996,763, and assigned to the assignee hereof and hereby expresslyincorporated by reference herein.

BACKGROUND

1. Field

The disclosed embodiments relate generally to the field ofcommunications, and more specifically to methods and apparatus foroperation of a forward link acknowledgement channel.

2. Background

The field of communications has many applications including, e.g.,paging, wireless local loops (WLL), Internet telephony, and satellitecommunication systems. An exemplary application is a cellular telephonesystem for mobile subscribers. Modern communication systems designed toallow multiple users to access a common communications medium have beendeveloped for such cellular systems. These communication systems may bebased on code division multiple access (CDMA), time division multipleaccess (TDMA), frequency division multiple access (FDMA), or othermultiple access techniques known in the art. These multiple accesstechniques decode and demodulate signals received from multiple users,thereby enabling simultaneous communication among multiple users andallowing for a relatively large capacity for the communication systems.

In the CDMA system, the available spectrum is shared efficiently among anumber of users, and techniques such as soft handoff are employed tomaintain sufficient quality to support delay-sensitive services (such asvoice) without wasting a lot of power. More recently, systems thatenhance the capacity for data services have also been available. Thesesystems provide data services by using higher order modulation, fasterpower control, faster scheduling, and more efficient scheduling forservices that have more relaxed delay requirements. An example of such adata-services communication system is the high data rate (HDR) systemthat conforms to the Telecommunications Industry Association/ElectronicIndustries Alliance (TIA/EIA) cdma2000 High Data Rate Air InterfaceSpecification IS-856, January 2002 (the IS-856 standard).

In a CDMA system, data transmission occurs from a source device to adestination device. The destination device receives the datatransmission, demodulates the signal, and decodes the data. As part ofthe decoding process, the destination device performs the CyclicRedundancy Code (CRC) check of the data packet to determine whether thepacket was correctly received. Error detection methods other than theuse of CRC, e.g., energy detection, can also be used in combination withor instead of CRC. If the packet was received with an error, thedestination device transmits a negative acknowledgement (NAK) message onits acknowledgement (ACK) channel to the source device, which respondsto the NAK message by retransmitting the packet that was received withan error.

Transmission errors may be particularly acute in applications with a lowsignal quality (e.g., low bit energy-to-noise power spectral densityratio (E_(b)/N_(o))). In this situation, a conventional dataretransmission scheme, such as Automatic Repeat Request (ARQ), may notmeet (or may be designed not to meet) the maximum bit error rate (BER)required for the system operation. In such a case, combining the ARQscheme with an error correction scheme, such as a Forward ErrorCorrection (FEC), is often employed to enhance performance. Thiscombination of ARQ and FEC is generally known as Hybrid ARQ (H-ARQ).

After transmitting a NAK, the destination device receives the datatransmission and retransmission, demodulates the signal, and separatesthe received data into the new packet and the retransmitted packet. Thenew packet and the retransmitted packet need not be transmittedsimultaneously. The destination device accumulates the energy of thereceived retransmitted packet with the energy already accumulated by thedestination device for the packet received with an error. Thedestination device then attempts to decode the accumulated data packet.However, if the packet frame is initially transmitted with insufficientenergy to permit correct decoding by the destination device, asdescribed above, and is then retransmitted, the retransmission providestime diversity. As a result, the total transmit energy of the frame(including retransmissions) is lower on average. The combined symbolenergy for both the initial transmission and retransmission(s) of theframe is lower than the energy that would have been required to transmitthe frame initially at full power (i.e., at a power level that wassufficient on its own to permit correct decoding by the destinationdevice) on average. Thus, the accumulation of the additional energyprovided by the subsequent retransmissions improves the probability of acorrect decoding. Alternately, the destination device might be able todecode the retransmitted packet by itself without combining the twopackets. In both cases, the throughput rate can be improved since thepacket received in error is retransmitted concurrently with thetransmission of the new data packet. Again, it should be noted that thenew packet and the retransmitted packet need not be transmittedsimultaneously.

In the reverse link (i.e., the communication link from the remoteterminal to the base station), the reverse supplemental channel (R-SCH)is used to transmit user information (e.g., packet data) from a remoteterminal to the base station, and to support retransmission at thephysical layer. The R-SCH may utilize different coding schemes for theretransmission. For example, a retransmission may use a code rate of ½for the original transmission. The same rate ½ code symbols may berepeated for the retransmission. In an alternative case, the underlyingcode may be a rate ¼ code. The original transmission may use ½ of thesymbols and the retransmission may use the other half of the symbols. Anexample of the reverse link architecture is described in detail in U.S.Patent Application No. 2002/0154610, entitled “REVERSE LINK CHANNELARCHITECTURE FOR A WIRELESS COMMUNICATION SYSTEM” assigned to theassignee of the present application.

In a CDMA communication system, and specifically in a system adapted forpacketized transmissions, congestion and overloading may reduce thethroughput of the system. The congestion is a measure of the amount ofpending and active traffic with respect to the rated capacity of thesystem. System overload occurs when the pending and active trafficexceeds the rated capacity. A system may implement a target congestionlevel to maintain traffic conditions without interruption, i.e., toavoid overloading and underloading of resources.

One problem with overloading is the occurrence of delayed transmissionresponses. An increase in response time often leads to application leveltimeouts, wherein an application requiring the data waits longer thanthe application is programmed to allow, producing a timeout condition.Applications will then needlessly resend messages on timeouts, causingfurther congestion. If this condition continues, the system might reacha condition where it can service no users. One solution (used in HDR)for this condition is congestion control. Another solution (used incdma2000) is proper scheduling.

The level of congestion in a system may be determined by monitoring thedata rates of pending and active users, and the received signal strengthrequired to achieve a desired quality of service. In a wireless CDMAsystem, the reverse link capacity is interference-limited. One measureof the cell congestion is the total amount of noise over the level ofthe thermal noise at a base station (referred to hereafter as the “riseover thermal” (ROT)). The ROT corresponds to the reverse link loading. Aloaded system attempts to maintain the ROT near a predetermined value.If the ROT is too high, the range of the cell (i.e., the distance overwhich the base station of the cell can communicate) is reduced and thereverse link is less stable. The range of the cell is reduced because ofan increase in the amount of transmit energy required to provide atarget energy level. A high ROT also causes small changes ininstantaneous loading that result in large excursions in the outputpower of the remote terminal. A low ROT can indicate that the reverselink is not heavily loaded, thus indicating that available capacity ispotentially being wasted.

However, operating the R-SCH with H-ARQ may require that the initialtransmission of an R-SCH frame not be power controlled very tightly tomeet the ROT constraints. Therefore, the delivered signal-to-noise ratio(SNR) on the initial transmission of an R-SCH frame can be below thelevel sufficient to permit correct decoding of the received data packet.This condition can result in a NAK message being transmitted over theforward link ACK channel.

Accordingly, from the discussion above, it should be apparent that thereis a need in the art for an apparatus and method that enables efficientoperation of the forward link ACK channel.

SUMMARY

Embodiments disclosed herein address the need for an apparatus andmethod that enables efficient operation of the forward link ACK channelin conjunction with a packet data channel in a wireless communicationssystem.

In one aspect, an acknowledgement method and apparatus of wirelesscommunication includes receiving a reverse supplemental channel (R-SCH)frame at a base station. The base station then transmits anacknowledgement (ACK) signal if quality of the received R-SCH frame isindicated as being good. A negative acknowledgement (NAK) signal istransmitted only if the received data frame is indicated as being badbut has enough energy such that, if combined with energy fromretransmission of the data frame, it would be sufficient to permitcorrect decoding of the data frame

In another aspect, an acknowledgement method and apparatus of wirelesscommunication includes transmitting a reverse supplemental channel(R-SCH) frame from a remote terminal to a base station. The base stationthen transmits a negative acknowledgement (NAK) signal to the remoteterminal if quality of the received R-SCH frame is indicated as beingbad. The remote terminal also recognizes that an absence of a receivedacknowledgement indicates an acknowledgement (ACK) signal such that thequality of the received R-SCH frame is good, which indicates a conditionwhere energy of the R-SCH frame is sufficient to permit correct decodingof the frame. The base station in this aspect is the best base stationthat provides smallest path loss to the remote terminal.

In another aspect, an acknowledgement channel for a wirelesscommunication system includes a block encoder, a mapper, and a mixer.The block encoder receives an ACK/NAK message having at least one bit,and operates to encode the ACK/NAK message with a generator matrix toproduce a codeword. The mapper maps the codeword into a binary signal.The mixer mixes the binary signal with an orthogonal spreading code suchas a Walsh code to produce an encoded ACK/NAK signal.

Other features and advantages of the present invention should beapparent from the following descriptions of the exemplary embodiments,which illustrates, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary wireless communication system thatsupports a number of users and is capable of implementing variousaspects of the invention;

FIG. 2 is a simplified block diagram of an embodiment of a base stationand a remote terminal of the FIG. 1 communication system;

FIG. 3 illustrates an exemplary forward link ACK channel according tothe acknowledgement scheme discussed herein;

FIG. 4 illustrates an exemplary forward link ACK channel operating inaccordance with an assumption that the remote terminal recognizes whichbase station is the best base station;

FIGS. 5A through 5C illustrate a flowchart of an exemplary method forimplementing an acknowledgement scheme operating on a forward link ACKchannel; and

FIG. 6 is block diagram of an exemplary F-CPANCH.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The term “exemplary”used throughout this description means “serving as an example, instance,or illustration,” and should not necessarily be construed as preferredor advantageous over other embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout these specific details. In some instances, well-known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the present invention.

In recognition of the above-stated need for an apparatus and method thatenables efficient operation of the forward link ACK channel, thisdisclosure describes exemplary embodiments for efficiently allocatingand utilizing the reverse link resources. In particular, a reliableacknowledgment scheme and an efficient retransmission scheme, which canimprove the utilization of the reverse link and allow data frames to betransmitted at lower transmit power, are described in detail below.

Although various aspects of the present invention will be described inthe context of a CDMA communications system, those skilled in the artwill appreciate that the techniques for providing efficient operation ofthe forward link ACK channel described herein are likewise suitable foruse in various other communications environments includingcommunications systems based on TDMA, FDMA, SDMA, PDMA, and othermultiple access techniques known in the art, and communications systemsbased on AMPS, GSM, HDR, and various CDMA standards, and othercommunication standards known in the art. Accordingly, any reference toa CDMA communications system is intended only to illustrate theinventive aspects of the present invention, with the understanding thatsuch inventive aspects have a wide range of applications.

FIG. 1 is a diagram of an exemplary wireless communication system 100that supports a number of users and capable of implementing variousaspects of the invention. The communication system 100 providescommunication for a number of cells, with each cell being serviced by acorresponding base station (BS) 104. Various remote terminals 106 aredispersed throughout the system 100. Individual base stations or remoteterminals will be identified by a letter suffix such as 104 a or 106 c.References to 104 or 106 without a letter suffix will be understood torefer to the base stations and remote terminals in the general sense.

Each remote terminal 106 may communicate with one or more base stations104 on the forward and reverse links at any particular moment, dependingon whether or not the remote terminal is active and whether or not it isin soft handoff. The forward link refers to transmission from a basestation 104 to a remote terminal 106, and the reverse link refers totransmission from a remote terminal 106 to a base station 104. As shownin FIG. 1, the base station 104 a communicates with the remote terminals106 a, 106 b, 106 c, and 106 d, and the base station 104 b communicateswith the remote terminals 106 d, 106 e, and 106 f. The remote terminal106 d is in a soft handoff condition and concurrently communicates withboth of the base stations 104 a and 104 b.

In the wireless communication system 100, a base station controller(BSC) 102 communicates with the base stations 104 and may furthercommunicate with a public switched telephone network (PSTN). Thecommunication with the PSTN is typically achieved via a mobile switchingcenter (MSC), which is not shown in FIG. 1 for simplicity. The BSC mayalso communicate with a packet network, which is typically achieved viaa packet data serving node (PDSN) that is also not shown in FIG. 1. TheBSC 102 provides coordination and control for the base stations 104. TheBSC 102 further controls the routing of telephone calls among the remoteterminals 106, and between the remote terminals 106 and userscommunicating with the PSTN (e.g., conventional telephones) and to thepacket network, via the base stations 104.

FIG. 2 is a simplified block diagram of an embodiment of a base station104 and a remote terminal 106, which are capable of implementing variousaspects of the invention. For a particular communication, voice data,packet data, and/or messages may be exchanged between the base station104 and the remote terminal 106. Various types of messages may betransmitted such as messages used to establish a communication sessionbetween the base station and the remote terminal and messages used tocontrol a data transmission (e.g., power control, data rate information,acknowledgment, and so on). Some of these message types are describedbelow. In particular, the implementation of the reverse link dataacknowledgement using the forward link ACK channel is described indetail.

For the reverse link, at the remote terminal 106, voice and/or packetdata (e.g., from a data source 210) and messages (e.g., from acontroller 230) are provided to a transmit (TX) data processor 212,which formats and encodes the data and messages with one or more codingschemes to generate coded data. Each coding scheme may include anycombination of cyclic redundancy check (CRC), convolutional, Turbo,block, and other coding, or no coding at all. Typically, voice data,packet data, and messages are coded using different schemes, anddifferent types of message may also be coded differently.

The coded data is then provided to a modulator (MOD) 214 and furtherprocessed (e.g., covered, spread with short PN sequences, and scrambledwith a long PN sequence assigned to the user terminal). The modulateddata is then provided to a transmitter unit (TMTR) 216 and conditioned(e.g., converted to one or more analog signals, amplified, filtered, andquadrature modulated) to generate a reverse link signal. The reverselink signal is routed through a duplexer (D) 218 and transmitted via anantenna 220 to the base station 104.

At the base station 104, the reverse link signal is received by anantenna 250, routed through a duplexer 252, and provided to a receiverunit (RCVR) 254. The receiver unit 254 conditions (e.g., filters,amplifies, downconverts, and digitizes) the received signal and providessamples. A demodulator (DEMOD) 256 receives and processes (e.g.,despreads, decovers, and pilot demodulates) the samples to providerecovered symbols. The demodulator 256 may implement a rake receiverthat processes multiple instances of the received signal and generatescombined symbols. A receive (RX) data processor 258 then decodes thesymbols to recover the data and messages transmitted on the reverselink. The recovered voice/packet data is provided to a data sink 260 andthe recovered messages may be provided to a controller 270. Theprocessing by the demodulator 256 and the RX data processor 258 arecomplementary to that performed at the remote terminal 106. Thedemodulator 256 and the RX data processor 258 may further be operated toprocess multiple transmissions received via multiple channels, e.g., areverse fundamental channel (R-FCH) and a reverse supplemental channel(R-SCH). Also, transmissions may be received simultaneously frommultiple remote terminals, each of which may be transmitting on areverse fundamental channel, a reverse supplemental channel, or both.

On the forward link, at the base station 104, voice and/or packet data(e.g., from a data source 262) and messages (e.g., from the controller270) are processed (e.g., formatted and encoded) by a transmit (TX) dataprocessor 264, further processed (e.g., covered and spread) by amodulator (MOD) 266, and conditioned (e.g., converted to analog signals,amplified, filtered, and quadrature modulated) by a transmitter unit(TMTR) 268 to generate a forward link signal. The forward link signal isrouted through the duplexer 252 and transmitted via the antenna 250 tothe remote terminal 106.

At the remote terminal 106, the forward link signal is received by theantenna 220, routed through the duplexer 218, and provided to a receiverunit 222. The receiver unit 222 conditions (e.g., downconverts, filters,amplifies, quadrature demodulates, and digitizes) the received signaland provides samples. The samples are processed (e.g., despreaded,decovered, and pilot demodulated) by a demodulator 224 to providesymbols, and the symbols are further processed (e.g., decoded andchecked) by a receive data processor 226 to recover the data andmessages transmitted on the forward link. The recovered data is providedto a data sink 228, and the recovered messages may be provided to thecontroller 230.

The reverse link has some characteristics that are very different fromthose of the forward link. In particular, the data transmissioncharacteristics, soft handoff behaviors, and fading phenomenon aretypically very different between the forward and reverse links. Forexample, the base station typically does not know a priori which remoteterminals have packet data to transmit, or how much data to transmit.Thus, the base station may allocate resources to the remote terminalswhenever requested and as available. Because of uncertainty in userdemands, the usage on the reverse link may fluctuate widely.

Apparatus and methods are provided to efficiently allocate and utilizethe reverse link resources in accordance with exemplary embodiments ofthe invention. The reverse link resources may be assigned via asupplemental channel (e.g., R-SCH) that is used for packet datatransmission. In particular, a reliable acknowledgment scheme and anefficient retransmission scheme are provided.

A reliable acknowledgment scheme and an efficient retransmission schemeshould consider several factors that control communication between basestations and a remote terminal. One of the factors to consider includethe fact that the base stations with path losses that are about a few dBlarger than a base station with the smallest path loss to the remoteterminal (e.g., the base station that is closest to the remoteterminal), but are in the Active Set of the remote terminal, haverelatively little chance of correctly receiving reverse supplementalchannel (R-SCH) frames.

In order for the soft handoff to work and the overall remote terminaltransmit power to be reduced, the remote terminal needs to receiveindications for these missed or bad R-SCH frames. Since the remoteterminal is going to receive significantly more negativeacknowledgements than positive acknowledgements, an exemplaryacknowledgement scheme is configured (see FIG. 3) so that the basestation (BS) sends a remote terminal (RT) an acknowledgement (ACK) for agood frame and a negative acknowledgement (NAK) for a bad frame only ifthe received bad R-SCH frame has enough energy such that, if combinedwith energy from the retransmission of the R-SCH frame, it would besufficient to permit correct decoding of the frame by the base station.The bad frames having insufficient energy (even when combined withretransmission energy) to permit correct decoding of the frame by thebase station, will not receive a NAK signal. Thus, when the remoteterminal does not receive an ACK or NAK signal, the remote terminal willassume that the bad frame received at the base station did not havesufficient energy to permit correct decoding of the frame. In this case,the remote terminal will need to retransmit the frame with a defaulttransmission level sufficient to permit correct decoding. In oneembodiment, this default transmission level may be predetermined toenable correct decoding by the base station. In another embodiment, thisdefault transmission level may be dynamically determined in accordancewith a transmission condition of the wireless CDMA system.

FIG. 3 illustrates an exemplary forward link ACK channel according tothe acknowledgement scheme discussed above. In the illustratedembodiment, the remote terminal sends an R-SCH frame to the basestation(s). The base station receives the R-SCH frame and sends an ACKsignal if the received R-SCH frame is recognized as being a “good”frame.

In one embodiment, the recognition of the quality of the received R-SCHframe (i.e., as being “good” or “bad”) can be made by observing thereverse link pilot signal, or, equivalently, based on the power controlbits sent from the remote terminal. Therefore, if the reverse link pilotsignal includes sufficient energy to permit correct decoding of theframe by the base station, the frame is considered to be “good”.Otherwise, if the reverse link pilot signal includes insufficient energyto permit correct decoding of the frame by the base station, the frameis considered to be “bad”.

The exemplary forward link ACK channel of the base station sends a NAKsignal with a traffic-to-pilot ratio (T/P) delta if the received R-SCHframe is recognized as being a “bad” frame but has enough energy tocombine with retransmission. This condition occurs when the received badR-SCH frame has enough energy such that if combined with energy from theretransmission of the R-SCH frame, it would be sufficient to permitcorrect decoding of the frame by the base station.

The traffic-to-pilot ratio (T/P) can be computed by measuring the ratiobetween the energy level of the reverse traffic channel (e.g., theR-SCH) and the reverse pilot channel. Thus, in this embodiment, thisratio is used for power control of the R-SCH and is compared to thetotal energy level sufficient to permit correct decoding of the R-SCHframe by the base station. The difference between the T/P value of theinitial transmission and the total energy level sufficient to permitcorrect decoding of the R-SCH frame provides a parameter referred to asa T/P delta. In general, the total energy level is the energy levelrequired to maintain a certain quality of service (QoS), which dependson speed, channel condition, and other parameters related to QoS.Accordingly, the T/P delta provides a differential energy value thatmust be delivered by the remote terminal on the retransmission tocompensate for the energy deficit on the initial transmission, and allowthe base station to correctly decode the R-SCH frame on the reverselink. The calculated T/P delta can be transmitted to the remote terminalon the forward ACK channel along with acknowledgement signals. In casewhere there are two or more base stations in the Active Set of theremote terminal, and both base stations send NAK signals with differentT/P deltas in response to bad R-SCH frames, the remote terminal shouldchoose the one with the lower T/P delta so that at least one basestation is allowed to correctly decode the packet.

Further, the base station will not send a NAK signal (i.e., NULL data)when the received bad R-SCH frame, combined with retransmission energy,has insufficient energy to permit correct decoding of the frame by thebase station. The remote terminal should recognize this “NULL” conditionas a signal from the base station to the remote terminal to retransmitthe R-SCH frame with a default transmission level sufficient to permitcorrect decoding.

The acknowledgement scheme illustrated in FIG. 3 can be furtheroptimized if the remote terminal can detect or determine which basestation has the smallest path loss to the remote terminal (i.e., thebest base station). In one embodiment, a pattern of power controlcommands from the base station to the remote terminal is used todetermine which base station is the best base station. For example, thebase station can measure the energy deficit of the actually receivedframe relative to the power control target (as is done in theclosed-loop power control) to determine which base station is the bestbase station. By averaging the energy deficit over many frames, the basestation can determine whether it is the best base station or not. Thisinformation can be transmitted to the remote terminal. For anotherexample, the base station can measure the pattern of power controlup/down bits to determine which is the best base station

In an alternative embodiment, the best base station can be readilydetermined if the remote terminal is operating in a data/voice (DV) modeof a 1xEv-DV system. In this mode, both the base station and the remoteterminal need to know which base station is the best base station. Thus,the remote terminal uses the reverse channel quality indicator channel(R-CQICH) to indicate to the base station the channel qualitymeasurements of the best base station.

However, using either embodiment described above, there may still be aperiod of time when the two sides (the base station and the remoteterminal) are not necessarily synchronized about which base station isthe best base station. Accordingly, in one embodiment, during the periodwhen there is a conflict between the two sides, the base station that isdesignated and undesignated as being the best base station is configuredto send both ACK (when the frame is good) and NAK (when the frame isbad) signals so that the remote terminal will not get confused.

FIG. 4 illustrates an exemplary forward link ACK channel operating inaccordance with an assumption that the remote terminal recognizes whichbase station is the best base station. Hence, in the illustratedembodiment, the remote terminal sends R-SCH frames to the best basestation and the secondary base station(s). Since the best base stationwill be receiving a lot more “good” frames than “bad” frames, theacknowledgement scheme from the best base station is biased toward notsending ACK signals for “good” frames but sending NAK signals for “bad”frames. The secondary base station will be biased in reverse since itwill be receiving a lot more “bad” frames than “good” frames. Thus, theacknowledgement scheme from the secondary base station is biased towardsending ACK signals for “good” frames but not sending NAK signals for“bad” frames.

Accordingly, in response to the receipt of the R-SCH frame from theremote terminal, the exemplary forward link ACK channel of the best basestation does not send an ACK signal (i.e., NULL data) if the receivedR-SCH frame is recognized as being a “good” frame. The remote terminalshould recognize this “NULL” condition as a signal from the best basestation that the transmitted R-SCH frame was received with sufficientenergy to permit correct decoding and that there is no need forretransmission of the frame. If the received R-SCH frame is recognizedas being a “bad” frame but has enough energy to combine withretransmission, the best base station sends a NAK signal with a T/Pdelta. This condition occurs when the received bad R-SCH frame hasenough energy such that if combined with energy from the retransmissionof the R-SCH frame, it would be sufficient to permit correct decoding ofthe frame by the best base station. The best base station sends a NAKsignal without a T/P delta if the received bad R-SCH frame, combinedwith retransmission energy, has insufficient energy to permit correctdecoding of the frame by the best base station. Thus, the remoteterminal retransmits the R-SCH frame with a default transmission levelsufficient to permit correct decoding.

However, the exemplary forward link ACK channel of the secondary basestation, in response to the receipt of the R-SCH frame from the remoteterminal, sends an ACK signal if the received R-SCH frame is recognizedas being a “good” frame. If the received R-SCH frame is recognized asbeing a “bad” frame but has enough energy to combine withretransmission, the secondary base station sends a NAK signal with a T/Pdelta. This condition occurs when the received bad R-SCH frame hasenough energy such that if combined with energy from the retransmissionof the R-SCH frame, it would be sufficient to permit correct decoding ofthe frame by the secondary base station. The secondary base station doesnot send a NAK signal (i.e., NULL data) when the received bad R-SCHframe, combined with retransmission energy, has insufficient energy topermit correct decoding of the frame by the base station. The remoteterminal should recognize this “NULL” condition as a signal from thesecondary base station to the remote terminal to retransmit the R-SCHframe with a default transmission level sufficient to permit correctdecoding.

An exemplary method for implementing an above-described acknowledgementscheme operating on a forward link ACK channel is illustrated in aflowchart shown in FIG. 5A through FIG. 5C. At box 500, a determinationis made as to whether the remote terminal under a condition where theterminal has knowledge about which base station has the smallest pathloss to the remote terminal (i.e., the best base station). As describedabove, this can be determined by measuring the energy deficit of theactually received frame relative to the power control target. Byaveraging the energy deficit over a sufficient number of frames, thebase station can determine whether it is the best base station or not.This information can be transmitted to the remote terminal. If theremote terminal is operating in a data/voice (DV) mode of a 1xEv-DVsystem, both the base station and the remote terminal must know whichbase station is the best base station. Thus, in the DV mode, there is noneed to determine which base station is the best base station.

If the remote terminal cannot determine which base station is the bestbase station at box 500, a “No” outcome, then a base station thatreceived the R-SCH frame sends an ACK signal (at box 504) if thereceived R-SCH frame is recognized as being a “good” frame. Therecognition of the quality of the received R-SCH frame (i.e., as being“good” or “bad”) can be made according to the process described above.

At box 506, a determination is made whether the received bad R-SCH framehas enough energy such that if combined with energy from theretransmission of the R-SCH frame, it would be sufficient to permitcorrect decoding of the frame by the base station. If this is the case,the exemplary forward link ACK channel of the base station sends a NAKsignal with a T/P delta, at box 508. Otherwise, the base station willnot send a NAK signal (i.e., NULL data) for the bad R-SCH frame, at box510. The remote terminal should recognize this “NULL” condition as asignal from the base station to the remote terminal to retransmit theR-SCH frame with a default transmission level sufficient to permitcorrect decoding.

If the remote terminal is able to determine which base station is thebest base station at box 500, a “Yes” outcome at box 500, then thesource of an ACK/NAK signal is determined, at 502, as being either the“best” base station or a “secondary” base station. If the source is the“best” base station, then the exemplary forward link ACK channel of thebest base station does not send an ACK signal (i.e., NULL data) inresponse to a “good” frame, at box 512. The remote terminal willrecognize this “NULL” condition as a signal from the best base stationthat the transmitted R-SCH frame was received with sufficient energy topermit correct decoding and that there is no need for retransmission ofthe frame.

At box 514, a determination is made whether the received bad R-SCH framehas sufficient energy such that if combined with energy from theretransmission of the R-SCH frame, correct decoding of the frame by thebase station could be performed. If this is the case, the exemplaryforward link ACK channel of the best base station sends a NAK signalwith a T/P delta, at box 516. Otherwise, the best base station sends aNAK signal without a T/P delta, at 518. Thus, the remote terminalretransmits the R-SCH frame with a default transmission level sufficientto permit correct decoding.

If the source of an ACK/NAK signal is determined (at box 502) to be thesecondary base station, then the exemplary forward link ACK channel ofthe secondary base station sends an ACK signal, at box 520, in responseto a “good” frame. At box 522, a determination is again made as towhether the received bad R-SCH frame has enough energy such that ifcombined with energy from the retransmission of the R-SCH frame, itwould be sufficient to permit correct decoding of the frame by the basestation. If this is the case, the exemplary forward link ACK channel ofthe secondary base station sends a NAK signal with a T/P delta, at box524. Otherwise, if the received bad R-SCH frame, combined withretransmission energy, has insufficient energy to permit correctdecoding of the frame by the base station, then the secondary basestation does not send a NAK signal (i.e., NULL data), at box 526. Theremote terminal should recognize this “NULL” condition as a signal fromthe secondary base station to the remote terminal to retransmit theR-SCH frame with a default transmission level sufficient to permitcorrect decoding.

As described above, acknowledgements (ACK) and negative acknowledgements(NAK) are transmitted by the base station for data transmission on theR-SCH. Moreover, the ACK/NAK can be transmitted using a Forward CommonPacket Acknowledgement Channel (F-CPANCH). FIG. 6 is a block diagram ofan exemplary F-CPANCH.

In one embodiment, ACK and NAK are transmitted as n-bit ACK/NAKmessages, with each message being associated with a corresponding dataframe transmitted on the reverse link. Thus, each ACK/NAK message mayinclude 1, 2, 3, or 4 bits (or possible more bits), with the number ofbits in the message being dependent on the number of reverse linkchannels in the service configuration. The n-bit ACK/NAK message may beblock coded to increase reliability or transmitted in the clear. Toimprove reliability, the ACK/NAK message for a particular data frame canbe retransmitted in a subsequent frame (e.g., 20 milliseconds later) toprovide time diversity for the message. The time diversity providesadditional reliability, or may allow for the reduction in power used tosend the ACK/NAK message while maintaining the same reliability. TheACK/NAK message may use error correcting coding as is well known in theart. For the retransmission, the ACK/NAK message may repeat the exactsame code word or may use incremental redundancy. The encoding approachis described in further detail below.

In the illustrated embodiment of FIG. 6, the F-CPANCH input for MACID=j, and k bits per 20 millisecond, where k=1, 2, 3, or 4, is providedto a (6, k) block encoder 602. In general, the (n, k) block codes arespecified in terms of their generator matrices. The encoder outputcodeword, y=[y₀y₁ . . . y_(n-1)], is equal to y=uG, where u=[u₀u₁ . . .u_(k-1)] is the input sequence, u₀ is the first input bit, y₀ is thefirst output bit, and G is the k×n generator matrix.

The generator matrix for the (6,1), F-CPANCH code is

G=[1 1 1 1 1 1].

The generator matrix for the (6,2), F-CPANCH code is

$G = {\begin{bmatrix}1 & 1 & 1 & 1 & 0 & 0 \\0 & 0 & 1 & 1 & 1 & 1\end{bmatrix}.}$

The generator matrix for the (6,3), F-CPANCH code is

$G = {\begin{bmatrix}1 & 0 & 1 & 1 & 0 & 0 \\0 & 1 & 0 & 1 & 1 & 0 \\0 & 0 & 1 & 0 & 1 & 1\end{bmatrix}.}$

The generator matrix for the (6,4), F-CPANCH code is

$G = {\begin{bmatrix}1 & 1 & 1 & 0 & 0 & 0 \\0 & 1 & 1 & 1 & 0 & 0 \\0 & 0 & 1 & 1 & 1 & 0 \\0 & 0 & 0 & 1 & 1 & 1\end{bmatrix}.}$

The output of the encoder 602 is then signal point mapped in a mapper604 such that a 0 is a +1 and a 1 is a −1. The resulting signal is mixedby a mixer 606 with a Walsh code, such as a 128-ary Walsh code (W¹²⁸).The use of a Walsh code provides for channelization and for resistanceto phase errors in the receiver. It should be noted that for other CDMAsystems, other orthogonal or quasi-orthogonal functions could besubstituted for Walsh code functions (e.g., OVSF for WCDMA).

To improve reliability, the ACK/NAK message for a particular data framecan be retransmitted in a subsequent frame (e.g., 20 milliseconds later)to provide time diversity for the message. The retransmission isimplemented by inserting a block 612, which provides a sequence delay ofone 20-millisecond frame, and a mapper 614 (substantially similar to themapper 604) and a mixer 616 (substantially similar to the mixer 606).However, the mixer 616 is mixed with a Walsh code starting at 65 andending at 128.

The outputs of the mixers 606 and 616 are combined by a summing element618. The output of the summing element 618 is then demultiplexed by ademulitiplexer 620 to produce an ACK/NAK signal having 384 symbols per20 milliseconds (19.2 ksps) appropriate for forward link transmission.

Table 1 gives the F-CPANCH code properties.

TABLE 1 F-CPANCH Code Properties Best possible Achieve Codewords Code(n, k) d_(min) dd_(min) Weight Number (6, 1) 6 6 0 1 6 1 (6, 2) 4 4 0 14 3 (6, 3) 3 3 0 1 3 4 4 3 (6, 4) 2 2 0 1 2 3 3 8 4 3 6 1

An efficient and reliable acknowledgement scheme can improve theutilization of the reverse link, and may also allow data frames to betransmitted at lower transmit power. For example, withoutretransmission, a data frame needs to be transmitted at a higher powerlevel (P₁) required to achieve one percent frame error rate (1% FER). Ifretransmission is used and is reliable, a data frame may be transmittedat a lower power level (P₂) required to achieve 10% FER. The 10% erasedframes may be retransmitted to achieve an overall 1% FER for thetransmission (i.e., 10%×10%=1%). Moreover, retransmission provides timediversity, which may improve performance. The retransmitted frame mayalso be combined with the initial transmission of the frame at the basestation, and the combined power from the two transmissions may alsoimprove performance. The recombining may allow an erased frame to beretransmitted at a lower power level.

Those of skill in the art will understand that method steps could beinterchanged without departing from the scope of the invention. Those ofskill in the art will also understand that information and signals mightbe represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill will further appreciate that the various illustrativelogical blocks, modules, circuits, and steps of a technique described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present invention.

The various illustrative logical blocks and modules described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or technique described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a subscriber station. In the alternative, the processor andthe storage medium may reside as discrete components in a subscriberstation.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit and scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method in a wireless communication system, comprising: receiving areverse link traffic channel data frame from a mobile terminal;transmitting an acknowledgement (ACK) signal by a base station providingthat a reverse link pilot signal includes sufficient energy to permitcorrect decoding of the data frame; and transmitting a negativeacknowledgement (NAK) signal by the base station providing that thereverse link pilot signal includes insufficient energy to permit correctdecoding of the data frame, but has enough energy such that if combinedwith energy from a retransmission of the data frame, it would besufficient to permit correct decoding of the data frame.
 2. The methodof claim 1, wherein the reverse link traffic channel is a reversesupplemental channel (R-SCH).
 3. The method of claim 1, furthercomprising: transmitting a traffic-to-pilot ratio (T/P) delta along withthe NAK signal.
 4. The method of claim 3, further comprising: adjustingan energy level of the data frame using the T/P delta.
 5. The method ofclaim 4, further comprising: retransmitting the adjusted data frame ifthe NAK signal is indicated.
 6. A base station for a wirelesscommunication system, the base station comprising: a receiver forreceiving a reverse link traffic channel data frame from a mobileterminal; and a transmitter to transmit an acknowledgement (ACK) signalproviding that a reverse link pilot signal includes sufficient energy topermit correct decoding of the data frame, and to transmit a negativeacknowledgement (NAK) signal providing that the reverse link pilotsignal includes insufficient energy to permit correct decoding of thedata frame, but has enough energy such that if combined with energy froma retransmission of the data frame, it would be sufficient to permitcorrect decoding of the data frame.
 7. The base station of claim 6,wherein the reverse link traffic channel is a reverse supplementalchannel (R-SCH).
 8. The base station of claim 6, wherein the transmittertransmits a traffic-to-pilot ratio (T/P) delta along with the NAKsignal.
 9. A wireless remote terminal for a communications system, theremote terminal comprising: a transmitter to transmit a reverse linktraffic channel data frame to a base station; and a receiver forreceiving an acknowledgement (ACK) signal from the base stationproviding that a reverse link pilot signal includes sufficient energy topermit correct decoding of the data frame, and to receive a negativeacknowledgement (NAK) signal from the base station providing that thereverse link pilot signal includes insufficient energy to permit correctdecoding of the data frame, but has enough energy such that if combinedwith energy from a retransmission of the data frame, it would besufficient to permit correct decoding of the data frame.
 10. Theterminal of claim 9, wherein the reverse link traffic channel is areverse supplemental channel (R-SCH).
 11. The terminal of claim 9,wherein the receiver receives a traffic-to-pilot ratio (T/P) delta alongwith the NAK signal.
 12. The terminal of claim 11, further comprising: acontroller for adjusting an energy level of the data frame using the T/Pdelta.
 13. The terminal of claim 12, wherein the transmitter retransmitsthe adjusted data frame if the NAK signal is indicated.
 14. An apparatusin a wireless communication system, comprising: means for receiving areverse link traffic channel data frame from a mobile terminal; meansfor transmitting an acknowledgement (ACK) signal by a base stationproviding that a reverse link pilot signal includes sufficient energy topermit correct decoding of the data frame; and means for transmitting anegative acknowledgement (NAK) signal by the base station providing thatthe reverse link pilot signal includes insufficient energy to permitcorrect decoding of the data frame, but has enough energy such that ifcombined with energy from a retransmission of the data frame, it wouldbe sufficient to permit correct decoding of the data frame.
 15. Theapparatus of claim 14, wherein the reverse link traffic channel is areverse supplemental channel (R-SCH).
 16. The apparatus of claim 14,further comprising: means for transmitting a traffic-to-pilot ratio(T/P) delta along with the NAK signal.
 17. The apparatus of claim 16,further comprising: means for adjusting an energy level of the dataframe using the T/P delta.
 18. The apparatus of claim 17, furthercomprising: means for retransmitting the adjusted data frame if the NAKsignal is indicated.